Multimedia processing technology is very widely applied to electronic products in the market, such as PDAs (Personal Digital Assistants), cellular phones, digital cameras, high-definition digital TVs and document cameras. For implementing the multimedia processing technology, DSP (Digital Signal Processor) is commonly used in these electronic products.
The DSP is advantageous of processing a large number of input digital signals at one time, and quickly executing operations to reach the Real-Time performance. The special DSP hardware and command designs facilitate the accomplishment of complicated control and various additional functions required by respective electronic products. Unlike the traditional microprocessor, the DSP has improved command execution speed, performance and Real-Time performance, so the DSP plays an important role on multimedia processing technology.
Taking a document camera as an example, it is popularly used in a regular meeting or an academic conference to show some literal or graphical data in order to facilitate the presentation or discussion of a document, chart or academic thesis. Compared with the traditional transparency projectors, the document cameras not only exhibit better image quality and versatile functions but also easier in preparing material to be shown. For example, the documents or charts do not have to be printed on the transparent projection slices as they used to do with the traditional transparency projector. Furthermore, a document camera is generally more compact is size than a traditional transparency projector and thus is inconvenient for carrying and storing.
A document camera is typically incorporated therein the architecture of a scanner or a video camera for performing digital image scanning, image capturing, and image outputting functions. So, a document camera may be equipped with a video-capturing module generally used in a digital still camera, digital video camera or cellular phone to execute the image pickup function. An image sensor, which is implemented with a complementary metal-oxide-semiconductor sensor (CMOS sensor) or a Charge Couple Device (CCD), is used in the video-capturing module to pick up the image of an object positioned in front of the video-capturing module, and an image display is used with the document camera for showing the image of the object captured by the image sensor. For example, the image display can be a monitor of a TV set, a display of a computer system or a projection screen showing images via the protection of a digital projector. In this way, the document or chart can be displayed in a live video manner. Also, the utilization of a document camera vivifies the presentation due to its functional varieties. Therefore, a document camera is expected to replace the traditional transparency projector in near future.
Please refer to the example shown in FIG. 1(a). A document camera 10 is coupled to a digital projector 20 and a projection screen 21 is arranged a proper distance from the digital projector 20. The image of the object 1 captured by a video-capturing module 11 is processed by the document camera 10 and then outputted to the digital projector 20 to be shown on the projection screen 21. By placing the object in of the focusable range of the video-capturing module 11, the document camera 10 will be able to process the image of object 1 and show it as a live video on the projection screen 21 via the digital projector 20. In addition to showing images via the digital projector 20 and the projection screen 21, the images captured by the document camera 10 can also be shown on an image display directly coupled to the document camera 10, such as a monitor of a TV set or a display of a computer system. For most document cameras, there is a focus adjusting device (not shown) arranged in the video-capturing module 11 for manually zooming in or zooming out the object 1 to focus on a specific area that the user is interested in.
Please refer to FIG. 1 (b). It shows a functional block diagram of the document camera 10. Conventionally, the document camera 10 includes a video-capturing module 101, a digital signal processor (DSP) 102 and a digital-to-analog converter (DAC) 103. The video-capturing module 101 includes an image-sensor 1011 and an analog-to-digital converter (ADC) 1012. In the image sensor 1011, the received light intensity from an object is converted into corresponding amount of charges through photoelectrical conversion and then outputted as an analog signal. The analog signal is then converted into a digital image data by the ADC 1012 and transmitted to the DSP 102 for further processing, e.g. zoom-in or zoom-out operations of the digital image data. Afterwards, the DAC 103 converts the processed digital image data into an analog image data and outputs it to an image display 104 for display.
Although zoom-in and zoom-out operations have been feasible in conventional document cameras, only a specific area of the object is shown the image display after the zoom-in or zoom-out operation. However, it is usually hard to figure out the position of the shown specific area relative to the full size image after a zoom-in operation. Particularly, the higher the zoom-in ratio is, the less recognizable the image becomes. Under this circumstance, the user generally needs to zoom in and out the image several times to locate the specific area in order to well perform a pan operation subsequently. It is apparently a time-wasting and inconvenient task for the user.